1. Field of the Invention
The invention relates to a printer head, in particular to an inkjet head having an electrostatic actuator and a manufacturing method of the same.
2. Description of the Related Art
Operation types for inkjet heads include a thermal type and a piezoelectric type. For the thermal type, a heater is installed which can supply heat into the chamber by which a substantially large amount of thermal energy may be supplied in a short period of time, and bubbles are formed in the ink in the chamber so that the ink is sprayed out through nozzles. However, there are problems in durability, caused by repeated impact due to the pressure from the bubbles created by the heat; it is difficult to control the size of ink droplets; and there is a limit to increasing the printing speed.
Meanwhile, the piezoelectric type utilizes the piezoelectric property, which is force being generated when voltage is supplied, by attaching piezoelectric material on a diaphragm to apply pressure to the chamber of the head, so that the pressure provided to the chamber pushes the ink out. Since it involves applying pressure in the chamber via force generated by the voltage supplied, it yields excellent performance in terms of speed and is thus widely used.
FIG. 1 is a cross sectional view of a conventional piezoelectric type inkjet head. As in FIG. 1, a conventional piezoelectric type inkjet head comprises a substrate 7, a diaphragm 8, a piezoelectric element 9, partitions 10, and a nozzle plate 1. In a piezoelectric type inkjet head with such a configuration, the piezoelectric element 9 mechanically expands and contracts when control signals are sent to the piezoelectric element 9 from a control signal generator 4, with the expanding and contracting of the piezoelectric element 9 causing the ink 5 in the chamber 2 to be pushed out of the nozzle 3 as discharged ink droplets 6.
However, piezoelectric type inkjet heads are expensive, because they use costly piezoelectric elements, and the yield is low due to a complicated manufacturing process, since the piezoelectric elements must be carefully coordinated with the electrodes, insulation layer, and protection layer, etc.
To overcome the above problems, inkjet heads that use electrostatic force are currently in use. These inkjet printer heads are fast becoming the inkjet head type of choice because of such advantages as ease in manufacture, low power consumption, and simple mechanism.
FIG. 2 is a cross sectional view of a conventional electrostatic type inkjet head, as shown in FIG. 1 of U.S. Pat. No. 5,894,316, illustrating an inkjet head having a diaphragm. As illustrated in FIG. 2, a conventional electrostatic type inkjet head comprises a glass plate 11, a lower substrate 13 mounted with a constant gap from the glass plate 11, an upper substrate 16 mounted on the upper face on which is formed a nozzle 15 for the passage of ink discharge, a center substrate 14 placed between the upper substrate 16 and the lower substrate 13 and mounted on both sides of the lower substrate 13, and an ink chamber 17 enclosed by the above and forming a chamber wherein ink is stored. As shown in FIG. 2, another electrode is mounted on the lower surface 13 facing the electrode 12 mounted on the glass plate 11 with a gap G in between.
In an electrostatic type inkjet head with such a configuration, the two electrodes are oppositely charged when power is supplied, so that there is an attraction force pulling each other. Therefore, the electrode mounted on the ink-storing chamber is pulled toward the other electrode 12. When the power is shut off, the pulled electrode returns to its original state, which applies pressure to the ink inside the chamber. This pressure causes the ink to be discharged through the nozzle to the exterior.
In such an electrostatic type inkjet printer head, the ink chamber on which pressure is applied must be formed to be greater than a certain size, and to increase the electrostatic force and lower the rigidity of the thin film which acts as the electrode, the electrodes must have a large area facing each other. This causes an increase in the occupied area per nozzle and the nozzle intervals are made wider, so that there is a limit to increasing the resolution of the printer and the manufacturing costs are increased. Also, additional metal must be deposited to form the electrodes, which causes the manufacturing process to be more complicated.
Examples of existing techniques to improve ink discharge pressure in electrostatic type inkjet heads include, first, Korean patent no. 10-0242157 (‘electrostatic actuator type inkjet printer head’). However, in this invention, the finger is protruded in one direction only, the diaphragm is pressurized by one electrostatic actuator, and the electrostatic actuator is secured only to the diaphragm, so that there is a limit to increasing electrostatic force.
A second example may be Japanese patent no. 2003-276194 (‘electrostatic actuator, droplet discharge head, and inkjet printer device’). However, in this invention, the finger is protruded in one direction only, the actuator body is not partitioned by the frame into individual components, and electrostatic force is increased by superposing several layers for the flat plates of the operation electrode and the fixed electrode, so that a large displacement is not always obtained depending on the distance between electrodes.